A relay node (RN), or simply relay, is considered as a tool to improve, e.g., the coverage of a base station, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas. The RN is wirelessly connected to a wireless communications network via a donor cell (also referred to as a donor enhanced Node B (donor eNB or D-eNB)) through network resources donated by the D-eNB.
Generally, there may be several different types of RNs, including an amplify-and-forward RN, wherein a RN receives a transmission and then transmits the received transmission without performing any attempt at demodulating and/or decoding the received transmission. The RN may receive and transmit the transmission over different frequency bands or over different intervals of time to reduce self-interference. An amplify-and-forward RN may amplify and/or apply additional signal processing on the received transmission to help improve communications system performance. Another type of RN is a decode-and-forward RN: such a RN receives a transmission, demodulates and decodes it, re-encodes and re-modulates it (possibly using a different modulation and coding scheme) and then transmits it.
Another concept applicable to RNs, either amplify-and-forward or decode-and-forward, is a two-way RN. In a two-way RN, there is typically no concept of uplink and/or downlink transmission. Instead, there may be multiple transmission phases. For example, there may be a first transmission phase (referred to herein as Multiple Access Phase (MA) wherein communications devices coupled to the two-way RN, such as an eNB and User Equipment (UE), transmit simultaneously, and a second transmission phase (referred to herein as Broadcast Phase (BC), wherein the two-way RN broadcasts signals to the eNB and UEs coupled to the two-way RN.
Information theory indicates that two-way RNs may provide better link efficiency than traditional one-way RNs (e.g., amplify-and-forward RNs and decode-and-forward RNs) that still use the concept of uplink and downlink transmission, thereby improving overall communications system performance.